format2.c

this is a gcc file, you can download it and learn its usetility, for further detail please look at t

// Test for format attributes: test applying them to types in C++.
// Origin: Joseph Myers <[e-mail]>
// { dg-do compile }
// { dg-options "-Wformat" }

__attribute__((format(printf, 1, 2))) void (*tformatprintf0) (const char *, ...);
void (*tformatprintf1) (const char *, ...) __attribute__((format(printf, 1, 2)));
void (__attribute__((format(printf, 1, 2))) *tformatprintf2) (const char *, ...);
void (__attribute__((format(printf, 1, 2))) ****tformatprintf3) (const char *, ...);

char * (__attribute__((format_arg(1))) *tformat_arg) (const char *);

void
baz (int i)
{
  (*tformatprintf0) ("%d", i);
  (*tformatprintf0) ((*tformat_arg) ("%d"), i);
  (*tformatprintf0) ("%"); // { dg-warning "format" "prefix" }
  (*tformatprintf0) ((*tformat_arg) ("%")); // { dg-warning "format" "prefix" }
  (*tformatprintf1) ("%d", i);
  (*tformatprintf1) ((*tformat_arg) ("%d"), i);
  (*tformatprintf1) ("%"); // { dg-warning "format" "postfix" }
  (*tformatprintf1) ((*tformat_arg) ("%")); // { dg-warning "format" "postfix" }
  (*tformatprintf2) ("%d", i);
  (*tformatprintf2) ((*tformat_arg) ("%d"), i);
  (*tformatprintf2) ("%"); // { dg-warning "format" "nested" }
  (*tformatprintf2) ((*tformat_arg) ("%")); // { dg-warning "format" "nested" }
  (****tformatprintf3) ("%d", i);
  (****tformatprintf3) ((*tformat_arg) ("%d"), i);
  (****tformatprintf3) ("%"); // { dg-warning "format" "nested 2" }
  (****tformatprintf3) ((*tformat_arg) ("%")); // { dg-warning "format" "nested 2" }
}